Both heated nozzles and probes are used to provide hot tip gating for injection molding. The difference between a nozzle and a probe is that the melt flows through a nozzle but around a probe. The increasing demand for more and more highly temperature sensitive materials has made it even more critical to monitor melt temperature as accurately as possible. U.S. Pat. No. 4,820,147 to Gellert which issued Apr. 11, 1989 relates to heated probes and shows inserting a thermocouple wire radially into one of the probe locating pins to monitor the melt temperature. More recently, Mold-Masters Limited Canadian Patent Application Serial Number 2,059,060-0 filed Jan. 20, 1992 entitled "Injection Molding Probe with Coaxial Thermocouple Sleeve and Heating Element" shows the thermocouple wire extending centrally in the probe. Thus the thermocouple is centrally located in the melt flow where heating and cooling is uniform on all sides.
However, in injection molding with nozzles where the melt flows through a central melt bore it previously was necessary to monitor the temperature at one side of the melt bore which has the disadvantage that it is not as accurate as monitoring it centrally in the melt flow. Injection molding nozzles having a torpedo with an elongated central shaft extending in alignment with a gate to provide hot tip gating are well known in the art. An early example in which the collar of the torpedo is seated in the mold to form a seal is shown in U.S. Pat. No. 4,450,999 to Gellert which issued May 29, 1984. An example in which the torpedo is retained in place in the nozzle by a separate gate insert is seen in the U.S. Pat. No. 5,028,227 to Gellert et al. which issued Jul. 2, 1991. While torpedoes have been successful for conducting heat to the gate area, they previously have also had the disadvantage that the operating temperature could only be monitored by a thermocouple located in the nozzle body on one side of the torpedo as seen in U.S. Pat. No. 5,028,227 mentioned above. Mold-Masters Limited Canadian Patent Application Serial Number 2,078,890-9 filed Sep. 22, 1992 entitled "Injection Molding Nozzle with Thermocouple Receiving Torpedo" does show a torpedo with a thermocouple positioned in the melt flow. However, it has the disadvantage that the radial thermocouple bore must extend through both the nozzle and the torpedo. Also, it is very important that the thermocouple element is accurately position and securely retained against the inner end of the radial bore and the only provision for this is a wire wrapped around the nozzle.
U.S. Pat. No. 4,875,848 to Gellert which issued Oct. 24, 1989, shows a nozzle with a threaded gate insert having a thermocouple bore extending inwardly through its hexagonal surface. However, the thermocouple element was only retained in place by friction which has not been found to be satisfactory.